Field of the Invention
The present invention relates to an internal combustion engine control apparatus provided with a heater control device for an exhaust gas sensor and more particularly to a heater control device that performs heater control while an internal combustion engine is in the automatic stop mode (idling stop mode).
Description of the Related Art
In order to achieve a low-carbon society, a technology for reducing the carbon dioxide (CO2) footprint has been desired also in the field of a vehicle internal combustion engine; in recent years, there has been actively developed, for example, a technology that automatically stops an internal combustion engine (brings the engine into the idling stop mode) so that the carbon dioxide footprint is reduced, while the vehicle is stopped and the engine is idled.
For example, Japanese Patent Application Laid-Open No. 2001-295678 discloses a technology that reduces the consumption amount of battery power by cutting off the supply of electric power to electric loads that need not to be operated while the internal combustion engine is in the automatic stop mode. In other words, by reducing the amount of power consumption while the internal combustion engine is stopped, there is decreased the necessary amount of generated electric power with which the battery is charged while the internal combustion engine is operated so that the load imposed on the internal combustion engine while the power generator generates electric power is reduced, whereby the amount of fuel consumption is decreased and hence the carbon dioxide footprint can be reduced.
Meanwhile, in the case where by use of an exhaust gas sensor in an internal combustion engine, the air-fuel ratio in an exhaust gas to be exhausted from the internal combustion engine is detected, it is required that the temperature of the sensor element is the activation temperature or higher; thus, in particular, the activation temperature is achieved by providing a heater and heating the sensor element. In this situation, in the case where the supply of electric power to the heater is cut off while the internal combustion engine is in the automatic stop mode, the temperature of the sensor element lowers to the activation temperature or lower; thus, when after the internal combustion engine ends its automatic stopping and then automatically starts, the temperature of the sensor element is increased up to the activation temperature, a long time elapses by the time the air-fuel ratio is detected and air-fuel ratio feedback is performed; therefore, there is posed a problem that the exhaust gas is deteriorated.
In order to cope with this problem, for example, Japanese Patent Application Laid-Open No. H09-88688 discloses a method in which while an internal combustion engine is in the automatic stop mode, the temperature of the sensor element is maintained at the activation temperature, and hence the air-fuel ratio is detected immediately after the internal combustion engine automatically starts and then the air-fuel ratio feedback is started so that the exhaust gas is prevented from being deteriorated.
Moreover, for example, Japanese Patent Application Laid-Open No. 2003-148206 discloses a method in which while the internal combustion engine is in the automatic stop mode, the temperature of the sensor element is maintained at a predetermined residual-heat temperature set to be lower than the activation temperature so that while the heater power consumption at a time when the internal combustion engine is in the automatic stop mode is suppressed, the time for raising the temperature of the sensor element up to the activation temperature after the internal combustion engine automatically starts is shortened, and the air-fuel ratio feedback is started at an earlier stage, whereby the exhaust gas is prevented from being deteriorated.
Still moreover, for example, in Japanese Patent Application Laid-Open No. 2009-156108, the longer is the air-fuel ratio detection undemanded period after the internal combustion engine automatically starts, the lower is set the residual-heat temperature to be maintained while the internal combustion engine is in the automatic stop mode, so that the amount of electric power supplied to the heater while the internal combustion engine is in the automatic stop mode is suppressed and, concurrently, the responsiveness to the air-fuel ratio detection demand to be issued after the internal combustion engine automatically starts is secured.
Furthermore, for example, Japanese Patent Application Laid-Open No. 2010-185345 discloses a heater control method in which an automatic stop period of an internal combustion engine is predicted and, based on the predicted automatic stop period, there is selected, as heater control at a time when the internal combustion engine is in the automatic stop mode, one (that causes a less amount of power consumption) of “the amount of power consumption of heater in the case where the temperature of the sensor element is maintained at a predetermined temperature (e.g., the activation temperature) while the internal combustion engine is in the automatic stop mode” and “the amount of power consumption of heater in the case where the supply of electric power to the heater is interrupted while the internal combustion engine is in the automatic stop mode and, after the internal combustion engine automatically starts, the supply of electric power to the heater is started again in order to raise the temperature of the sensor element to the predetermined temperature” so that the amount of power consumption becomes smaller.
Meanwhile, for the purpose of maintaining the temperature of the sensor element of an internal-combustion-engine exhaust gas sensor at the activation temperature, there is proposed a method in which attention is paid to the relationship between the real temperature and the impedance of the sensor element of the exhaust gas sensor, the real temperature of the sensor element is estimated from the impedance thereof, and then the effective voltage to be applied to the heater is adjusted in such a way that the estimated real temperature of the sensor element becomes a desired activation temperature. However, as time elapses, due to its exposure to the exhaust gas or due to materials adhered to it, the sensor element deteriorates and hence the relationship between the real temperature and the impedance of the sensor element deviates from that of an initially-middle-impedance sensor element 3002, as an impedance-deteriorated sensor element 3004 in FIG. 30(a); thus, there is produced an error in the estimation of the real temperature of the sensor element based on the impedance thereof. As a result, the desired activation temperature cannot be maintained, and the real temperature of the sensor element becomes higher than the desired activation temperature; therefore, there is posed a problem that the amount of power consumption increases or a problem that the sensor element or the heater is overheated.
The variation in the characteristics of the sensor element also makes the relationship between the real temperature and the impedance of the sensor element differ from that of the initially-middle-impedance sensor element 3002, for example, as an initially-lower-limit-impedance sensor element 3001 in FIG. 30(a); therefore, because there is produced an error in the estimation of the real temperature of the sensor element based on the impedance thereof, the desired activation temperature cannot be maintained, and the real temperature of the sensor element becomes lower than the desired activation temperature. As a result, the air-fuel ratio control cannot be performed, or the accuracy of the air-fuel ratio control is deteriorated, whereby there is posed a problem that the exhaust gas is deteriorated.
With regard to these problems, for example, Japanese Patent Application Laid-Open No. 2000-65784 discloses a method in which the integrated amount of electric power, supplied to a heater under a predetermine driving mode (at least one of the cold ordinary idling mode of the internal combustion engine, the completely warmed-up ordinary idling mode, and the completely warmed-up ordinary traveling mode) and during a predetermined period, is adopted, as a parameter of the deterioration of the sensor element caused as time elapses, and the impedance of the sensor element is corrected so that the temperature of the sensor element can appropriately be controlled so as to become a control target value and hence overheating of the sensor element or the heater can be prevented.